Re: [PATCH 2/4] mm: add new mmget() helper

[Michal Hocko <mhocko@kernel.org>]

On Fri 16-12-16 09:22:00, Vegard Nossum wrote:
> Apart from adding the helper function itself, the rest of the kernel is
> converted mechanically using:
> 
>   git grep -l 'atomic_inc.*mm_users' | xargs sed -i 's/atomic_inc(&\(.*\)->mm_users);/mmget\(\1\);/'
>   git grep -l 'atomic_inc.*mm_users' | xargs sed -i 's/atomic_inc(&\(.*\)\.mm_users);/mmget\(\&\1\);/'
> 
> This is needed for a later patch that hooks into the helper, but might be
> a worthwhile cleanup on its own.

Same here a clarification comment would be really nice

/**
 * mmget: pins the address space
 *
 * Makes sure that the address space of the given mm struct doesn't go
 * away. This doesn't protect from freeing parts of the address space
 * though.
 *
 * Never use this function if the time the address space is pinned is
 * not bounded.
 */

> 
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Michal Hocko <mhocko@suse.com>
> Signed-off-by: Vegard Nossum <vegard.nossum@oracle.com>

Acked-by: Michal Hocko <mhocko@suse.com>

> ---
>  arch/arc/kernel/smp.c           |  2 +-
>  arch/blackfin/mach-common/smp.c |  2 +-
>  arch/frv/mm/mmu-context.c       |  2 +-
>  arch/metag/kernel/smp.c         |  2 +-
>  arch/sh/kernel/smp.c            |  2 +-
>  arch/xtensa/kernel/smp.c        |  2 +-
>  include/linux/sched.h           |  5 +++++
>  kernel/fork.c                   |  4 ++--
>  mm/swapfile.c                   | 10 +++++-----
>  virt/kvm/async_pf.c             |  2 +-
>  10 files changed, 19 insertions(+), 14 deletions(-)
> 
> diff --git a/arch/arc/kernel/smp.c b/arch/arc/kernel/smp.c
> index 9cbc7aba3ede..eec70cb71db1 100644
> --- a/arch/arc/kernel/smp.c
> +++ b/arch/arc/kernel/smp.c
> @@ -124,7 +124,7 @@ void start_kernel_secondary(void)
>  	/* MMU, Caches, Vector Table, Interrupts etc */
>  	setup_processor();
>  
> -	atomic_inc(&mm->mm_users);
> +	mmget(mm);
>  	mmgrab(mm);
>  	current->active_mm = mm;
>  	cpumask_set_cpu(cpu, mm_cpumask(mm));
> diff --git a/arch/blackfin/mach-common/smp.c b/arch/blackfin/mach-common/smp.c
> index bc5617ef7128..a2e6db2ce811 100644
> --- a/arch/blackfin/mach-common/smp.c
> +++ b/arch/blackfin/mach-common/smp.c
> @@ -307,7 +307,7 @@ void secondary_start_kernel(void)
>  	local_irq_disable();
>  
>  	/* Attach the new idle task to the global mm. */
> -	atomic_inc(&mm->mm_users);
> +	mmget(mm);
>  	mmgrab(mm);
>  	current->active_mm = mm;
>  
> diff --git a/arch/frv/mm/mmu-context.c b/arch/frv/mm/mmu-context.c
> index 81757d55a5b5..3473bde77f56 100644
> --- a/arch/frv/mm/mmu-context.c
> +++ b/arch/frv/mm/mmu-context.c
> @@ -188,7 +188,7 @@ int cxn_pin_by_pid(pid_t pid)
>  		task_lock(tsk);
>  		if (tsk->mm) {
>  			mm = tsk->mm;
> -			atomic_inc(&mm->mm_users);
> +			mmget(mm);
>  			ret = 0;
>  		}
>  		task_unlock(tsk);
> diff --git a/arch/metag/kernel/smp.c b/arch/metag/kernel/smp.c
> index af9cff547a19..c622293254e4 100644
> --- a/arch/metag/kernel/smp.c
> +++ b/arch/metag/kernel/smp.c
> @@ -344,7 +344,7 @@ asmlinkage void secondary_start_kernel(void)
>  	 * All kernel threads share the same mm context; grab a
>  	 * reference and switch to it.
>  	 */
> -	atomic_inc(&mm->mm_users);
> +	mmget(mm);
>  	mmgrab(mm);
>  	current->active_mm = mm;
>  	cpumask_set_cpu(cpu, mm_cpumask(mm));
> diff --git a/arch/sh/kernel/smp.c b/arch/sh/kernel/smp.c
> index ee379c699c08..edc4769b047e 100644
> --- a/arch/sh/kernel/smp.c
> +++ b/arch/sh/kernel/smp.c
> @@ -179,7 +179,7 @@ asmlinkage void start_secondary(void)
>  
>  	enable_mmu();
>  	mmgrab(mm);
> -	atomic_inc(&mm->mm_users);
> +	mmget(mm);
>  	current->active_mm = mm;
>  #ifdef CONFIG_MMU
>  	enter_lazy_tlb(mm, current);
> diff --git a/arch/xtensa/kernel/smp.c b/arch/xtensa/kernel/smp.c
> index 9bf5cea3bae4..fcea72019df7 100644
> --- a/arch/xtensa/kernel/smp.c
> +++ b/arch/xtensa/kernel/smp.c
> @@ -135,7 +135,7 @@ void secondary_start_kernel(void)
>  
>  	/* All kernel threads share the same mm context. */
>  
> -	atomic_inc(&mm->mm_users);
> +	mmget(mm);
>  	mmgrab(mm);
>  	current->active_mm = mm;
>  	cpumask_set_cpu(cpu, mm_cpumask(mm));
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 31ae1f49eebb..2ca3e15dad3b 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -2899,6 +2899,11 @@ static inline void mmdrop_async(struct mm_struct *mm)
>  	}
>  }
>  
> +static inline void mmget(struct mm_struct *mm)
> +{
> +	atomic_inc(&mm->mm_users);
> +}
> +
>  static inline bool mmget_not_zero(struct mm_struct *mm)
>  {
>  	return atomic_inc_not_zero(&mm->mm_users);
> diff --git a/kernel/fork.c b/kernel/fork.c
> index 997ac1d584f7..f9c32dc6ccbc 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -989,7 +989,7 @@ struct mm_struct *get_task_mm(struct task_struct *task)
>  		if (task->flags & PF_KTHREAD)
>  			mm = NULL;
>  		else
> -			atomic_inc(&mm->mm_users);
> +			mmget(mm);
>  	}
>  	task_unlock(task);
>  	return mm;
> @@ -1177,7 +1177,7 @@ static int copy_mm(unsigned long clone_flags, struct task_struct *tsk)
>  	vmacache_flush(tsk);
>  
>  	if (clone_flags & CLONE_VM) {
> -		atomic_inc(&oldmm->mm_users);
> +		mmget(oldmm);
>  		mm = oldmm;
>  		goto good_mm;
>  	}
> diff --git a/mm/swapfile.c b/mm/swapfile.c
> index f30438970cd1..cf73169ce153 100644
> --- a/mm/swapfile.c
> +++ b/mm/swapfile.c
> @@ -1402,7 +1402,7 @@ int try_to_unuse(unsigned int type, bool frontswap,
>  	 * that.
>  	 */
>  	start_mm = &init_mm;
> -	atomic_inc(&init_mm.mm_users);
> +	mmget(&init_mm);
>  
>  	/*
>  	 * Keep on scanning until all entries have gone.  Usually,
> @@ -1451,7 +1451,7 @@ int try_to_unuse(unsigned int type, bool frontswap,
>  		if (atomic_read(&start_mm->mm_users) == 1) {
>  			mmput(start_mm);
>  			start_mm = &init_mm;
> -			atomic_inc(&init_mm.mm_users);
> +			mmget(&init_mm);
>  		}
>  
>  		/*
> @@ -1488,8 +1488,8 @@ int try_to_unuse(unsigned int type, bool frontswap,
>  			struct mm_struct *prev_mm = start_mm;
>  			struct mm_struct *mm;
>  
> -			atomic_inc(&new_start_mm->mm_users);
> -			atomic_inc(&prev_mm->mm_users);
> +			mmget(new_start_mm);
> +			mmget(prev_mm);
>  			spin_lock(&mmlist_lock);
>  			while (swap_count(*swap_map) && !retval &&
>  					(p = p->next) != &start_mm->mmlist) {
> @@ -1512,7 +1512,7 @@ int try_to_unuse(unsigned int type, bool frontswap,
>  
>  				if (set_start_mm && *swap_map < swcount) {
>  					mmput(new_start_mm);
> -					atomic_inc(&mm->mm_users);
> +					mmget(mm);
>  					new_start_mm = mm;
>  					set_start_mm = 0;
>  				}
> diff --git a/virt/kvm/async_pf.c b/virt/kvm/async_pf.c
> index efeceb0a222d..9ec9cef2b207 100644
> --- a/virt/kvm/async_pf.c
> +++ b/virt/kvm/async_pf.c
> @@ -200,7 +200,7 @@ int kvm_setup_async_pf(struct kvm_vcpu *vcpu, gva_t gva, unsigned long hva,
>  	work->addr = hva;
>  	work->arch = *arch;
>  	work->mm = current->mm;
> -	atomic_inc(&work->mm->mm_users);
> +	mmget(work->mm);
>  	kvm_get_kvm(work->vcpu->kvm);
>  
>  	/* this can't really happen otherwise gfn_to_pfn_async
> -- 
> 2.11.0.1.gaa10c3f
> 

-- 
Michal Hocko
SUSE Labs

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